Stiffness of compression testing machines

A ring test with six participating laboratories and rubber stoppers as refe rence material was performed to monitor the performance of commercial compr ession resting instruments. Testing conditions were chosen to be in the ran ge of regular compression testing. Small, single screw instruments with a c antilever exhibited a significant deviation in the force/deformation-respon se compared with double-screw instruments with a crosshead. Additional test s made with an external device for displacement recording revealed that the se differences have to be attributed to insufficient stiffness and some com pliance in the cantilever of the tested single-screw instruments. Some cons equences of the test results for experiments on soft, semi-soft and rigid f ood materials are discussed and an equation is developed to correct for the flexing of the cantilever beam in the single screw machine.